This is a Phase 1/2a, open-label, multi-center, sequential dose escalation, safety study of Plasmin (Human) in acute ischemic stroke caused by middle cerebral artery occlusion documented by arteriography. Plasmin (Human) will be administered through a catheter into the thrombus within 9 hours of stroke onset. Approximately sixty-one (61) patients will be enrolled and will receive Plasmin (Human). The objectives of this study are to determine the safety of escalating doses of Plasmin (Human) and to determine the proportion of patients with treatment success, defined as partial or full recanalization.